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Re: "Disappearing" Getter Question

Okay, here's my understanding - which I would be GLAD for someone to correct if I'm wrong.

Since the barium (that's the usual material in receiving tubes) deposited on the glass got there when it condensed, the barium has a specific amount of mass. The barium was heated to a gaseous state ("flashed") when the tube was made, and the gas condensed on the cooler glass outer surface of the tube. So while small, there is mass in the getter flash deposit.

When a gas molecule (other than the inert "noble" gases) comes in contact with the barium it is absorbed and held. Therefore the mass of the getter increases as it "disappears". But the material must still be within the tube glass envelope.

Which leaves only two possibilities as I see it:

1. The getter barium (now barium oxide or some other compound) is present in the tube in very small solid particles, or...

2. The getter barium (now barium oxide or some other compound) is present in the tube in a gaseous state. For this to occur it seems to me the gas formed by getter "evaporation" would have to be a "noble" gas (like helium, for instance - a gas that will not chemically react with any other element) that can circulate harmlessly in the tube.

Any physicists in the audience today??


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